The present invention relates to control of power in overhead line electrical distribution systems and in particular to an operating mechanism for mechanically interlocking the circuit-breaker element of an autorecloser with an associated disconnector to prevent on-load operation of the disconnector.
Autoreclosers of the type referred to in this specification are intended to be mounted on electricity distribution poles and pylons in overhead line electrical distribution systems. Pole mounted Autoreclosers are in effect, pole mounted circuit breakers connected to control the power flowing in overhead lines. Systems of this type are prone to electrical faults of a transient nature, due to wind blown foliage, birds and lightning strikes Therefore Autoreclosers, as their name suggests, are arranged to open and clear fault current when it reaches a predetermined level, and then reclose after a pre-deteried time interval. In cases where the electrical fault, which causes the autorecloser to open, self-clears during the cessation of current, safe power supply is re-established when the unit recloses. However. Autoreclosers are designed to remain in the open position, preventing further electrical current flow, when they have experienced the passage of a pre-determined number of electrical fault currents in a pre-determined sequence of operations. These sequences are usually a selection of instantaneous and fault current dependent time opening operations. When an autorecloser has exhausted its pre-set sequence the fault is deemed to be permanent and it is said to have xe2x80x98locked-outxe2x80x99 in the OPEN position. The system then requires manual intervention to carry out repairs at the site of the fault.
When repairs are to be carried out to the overhead line, operator safety dictates that the line be isolated from the system by the use of a disconnector and i live-line working is not to be employed, the faulted section is earthed. These disconnectors are off-load switching devices They provide an isolating gap between their contacts capable of withstanding a much higher impulse voltage level than the impulse voltage which the overhead line itself can withstand, and so provide protection from electrical flashover of one side of the overhead line system to the other. As these are off-load switching devices they have to be interlocked with the circuit-breaker element of the autorecloser to prevent on-load operation.
The present invention provides an improved form of mechanical interlock between the circuit breaker element of an autorecloser and a disconnector.
According to the present invention, an operating mechanism for an autorecloser, in which a circuit breaker is in electrical series with a disconnector, comprises shaft means for transmitting motion between first and second ends thereof, the first end being connected to the circuit breaker for moving a moveable contact of the circuit breaker between CLOSED and OPEN positions, the second end being, adapted to engage a profile of a rotary crank means, the rotary crank means being attached to means for rotating it the rotary crank means being further attached to an insulating linkage for moving a moveable contact of the disconnector between CLOSED and OPEN positions, the arrangement being such that when the rotary crank means is rotated in a predetermined direction through a first predetermined angle from a starting position in which the moveable contacts of the circuit breaker and the disconnector are both in the CLOSED position, the moveable contact of the circuit breaker is moved to an OPEN position while the moveable contact of the disconnector is maintained in the CLOSED position and during further rotation of the rotary crank means in the first direction through a second predetermined angle. the moveable contact of the disconnector is moved to an OPEN position while the moveable contact of the circuit breaker is maintained in the OPEN position and further that when the rotary crank means is rotated back to its starting position. the moveable contact of the disconnector is moved back to its CLOSED position before the moveable contact of the circuit breaker is moved back to its CLOSED position.
In order to move the moveable contact of the circuit breaker from the CLOSED to the OPEN position, the profile of the rotary crank means may include a first portion adapted to exert a lever action on the second end of the shaft means during rotation of the rotary crank means through the first predetermined angle.
The profile of the rotary crank means advantageously further includes a second portion adjacent the first portion the second portion comprising a sector having a constant radius over an angle at least substantially equal to the second predetermined angle, whereby the moveable contact of the circuit breaker is maintained in the OPEN position during the further rotation of the rotary crank means through the second predetermined angle.
Conveniently, the means for rotating the rotary crank means comprises a link attached to the rotary crank means at a fixed radial distance from the center of rotation of the rotary crank means.
The moveable contact of the disconnector may comprise a contactor link hinged at one end thereof to fixed contact means so that an opposing free end of the contactor link can be moved into and out of engagement with further fixed contact means thereby respectively to CLOSE and OPEN the disconnector. This may be achieved by pivotally connecting the contactor link at a location between its hinged end and its tree end to an end of the insulating linkage which at an opposed end thereof is pivotally connected to the rotary crank means at a location thereon which is a fixed radial distance from the center of rotation of the rotary crank means and a fixed angular distance from the first portion of the profile of the rotary crank means.
The shaft means is conveniently also part of an actuator element of the autorecloser for automatically driving the moveable contact of the circuit breaker into its OPEN and CLOSED states.